While late gadolinium enhanced (LGE) MRI is the gold standard for detection of focal myocardial scarring [1], it is less effective than cardiac T1 mapping (ECV) for detection of diffuse fibrosis. LGE, in principle, can be synthesized from cardiac T1 maps. We sought to derive synthetic LGE images from saturation-recovery based cardiac T1 maps for simultaneous assessment of focal and diffuse cardiac fibrosis.

We imaged 6 mongrel dogs with lesions created by RF ablation on a 3T MRI system (Verio, Siemens), using arrhythmia-insensitive-rapid (AIR) cardiac T1 mapping [2] and standard LGE MRI during equilibrium of Gd-BOPTA (slow infusion at 0.002 mmol/kg/min), in order to compare standard and synthetic LGE images acquired at identical concentration of Gd-BOPTA. Both LGE MRI and cardiac T1 mapping were acquired with identical spatial resolution = 1.4×1.4×7 mm. After calculating the AIR cardiac T1 maps, as previously described[2], a synthetic LGE image was subsequently synthesized using the Bloch equation describing an ideal inversion recovery: Mz = 1 - 2*exp(-TI/T1), where Mz is the longitudinal magnetization, inversion time (TI) to null the normal myocardium was calculated by rearranging the above equation as TI = T1M × log(2), where T1M is the mean T1 of normal myocardium. For quantitative analysis, we calculated the contrast ratio, as defined as the signal difference (e.g., lesion-myocardium) divided by lesion (see Table 1). Same analysis was performed for the blood-myocardium pair. This analysis enabled us to compare standard and synthetic LGE data sets with different intensity scales. Pair-wise t-test was used to compare the two groups (standard vs. synthetic LGE).

Table 1

Summary of contrast ratio of lesion-myocardium and blood-myocardium pairs.

We propose a new approach to simultaneously assess focal and diffuse cardiac fibrosis using cardiac T1 mapping, with no need for separate acquisition of standard LGE images. This approach is also compatible with inversion-recovery based cardiac T1 mapping methods. Synthetic LGE derived from T1 mapping may be particularly useful for infarct size and area at risk calculations, because it is inherently insensitive to signal variation due to confounders such as RF excitation and receive inhomogeneities.

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